Many variations occur in the ophthalmoscopic appearance of the peripheral neural retina. In most cases, these variations are not of clinical significance; however, certain anatomical changes can render eyes at higher risk for retinal breaks and rhegmatogenous retinal detachment. In order to detect and diagnose pathology versus normal variation in the anterior retina accurately, it is of critical importance to be aware of the normal anatomical appearance of this area.

The fundus may be roughly separated into central (posterior) and peripheral (anterior) portions by a circle that passes through the posterior edge of the scleral entrance of each vortex vein ampulla. The anatomical equator is located approximately two disc diameters (3?mm) anterior to the entrance of the scleral canals. Thus, the vortex veins become important landmarks when separating the peripheral fundus from the posterior pole.

The fundus also may be divided by natural features into superior and inferior halves by the long ciliary nerves and arteries that form a horizontal boundary nasally and temporally.[1]

In the peripheral fundus it often is difficult or impossible to distinguish between arterioles and venules on the basis of size, color, or pattern. [2] The most practical method of identification is to trace the vessels back to the posterior fundus. The retinal arterioles and venules generally do not course together but are evenly distributed throughout the periphery. The majority become very small and disappear before reaching a distance of 0.5 disc diameter from the ora serrata. The arteries disappear first, whereas the venules tend to extend closer toward the ora serrata.

Ora Serrata

In the ora serrata region, the retina becomes opalescent and often is marked by small rows of cystoid cavities.[3] This is normal—extensive cystoid changes do not represent pathology. The underlying

pigment epithelium appears darker and more granular than that seen posteriorly. The neural retina stops abruptly at the ora serrata and is continued by the nonpigmented ciliary epithelium, which appears considerably thinner than the retina. The pars plana corporis ciliaris is more deeply pigmented than the peripheral retina and, thus, the choroidal pattern is obscured by that of the pigment epithelium. The development of the ora serrata is incomplete at birth and continues during early life.[4] [5]

Because ora bays and teeth (or dentate processes) frequently are difficult to identify temporally, the exact number of ora teeth is not easy to calculate. Salzmann[5] in 1912 identified 48, whereas Straatsma et al.[6] noted 16 dentate processes along the average ora serrata. In the author’s experience the number varies, but usually between 20 and 30 dentate processes can be counted reliably, corresponding in position to the intervals between the ciliary processes. Occasionally, two oral teeth join to form an enclosed oral bay, which may be confused with a retinal hole ( Fig. 134-1 ). Oral bays do not carry an increased risk for rhegmatogenous retinal detachment.

Vitreous Base

One of the most significant structures in the peripheral fundus is the vitreous base. It is of clinical importance because retinal

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Figure 134-2 The anterior border and posterior border of the vitreous base. The posterior border is irregular. Areas of paving stone degeneration that extend across the ora serrata into the pars plana can also be seen.

breaks frequently occur along its posterior border and, in the case of traumatic detachment, occasionally along the anterior border, as well.[7] The vitreous base involves the full circumference of the peripheral fundus and measures approximately 3.2?mm in width. Generally, it is wider nasally than temporally and may have an irregular posterior border ( Fig. 134-2 ). It represents an area in the fundus in which the vitreous, neural retina, and pigment epithelium all are firmly adherent, one to the other. It is for this reason that in some cases of traumatic detachment the vitreous base is avulsed with its underlying neural retina and pigment epithelium, to create a retinal dialysis and a “garland” that hangs down into the vitreous cavity. The vitreous base may be prominent in some individuals, especially those with a darkly pigmented choroid.

The pars plana is delineated at its posterior margin by the ora serrata. The sensory retina continues into the pars plana as the nonpigmented ciliary epithelium. The vitreous base, which straddles the ora serrata, has its anterior border in the pars plana, where it parallels the configuration of the ora serrata.

OCULAR MANIFESTATIONS AND DIAGNOSIS OF PERIPHERAL RETINAL LESIONS

Meridional Folds or Radial Folds

Meridional folds, or radial folds, which usually involve all neural retinal layers, are a common, normal variant seen in the peripheral fundus. As a rule, a meridional fold begins in the ora serrata and runs posteriorly and perpendicularly to it in a meridional fashion. It is a radially aligned elevation of the peripheral retina and may be associated with retinal breaks ( Fig. 134-3 ). Meridional folds are found significantly more often nasally than temporally and especially in the upper nasal quadrant.[3] [8] They occur in 20% of eyes examined during autopsy.[9] In cases of rhegmatogenous retinal detachment, the posterior edges of meridional folds must be examined carefully for retinal breaks.

Meridional Complex

Occasionally, meridional folds extend to the posterior aspect of a ciliary process. The configuration is called a meridional complex (see Fig. 134-1 ). The fundamental and consistent feature of a meridional complex is an atypical dentate process that aligns with a ciliary process. Both meridional folds and meridionally aligned complexes can be the sites of small retinal breaks and require careful examination in patients who have retinal detachment (see Fig. 134-3 ).

Figure 134-3 Meridional fold with a small break at the base of the fold.

Figure 134-4 Pars plana cysts. The radial striations can also be seen directed between the ciliary processes. (Courtesy of Dr. Ralph Eagle, Jr.)

Pars Plana Cysts

Cysts of the pars plana corporis ciliaris are another variant seen in the fundus periphery.[10] These consist of a clear cystoid space between the pigmented and nonpigmented epithelium located anterior to the ora serrata ( Fig. 134-4 ). The cysts, which have the appearance of half-inflated balloons, lie between the pars plana radiations. Generally, the overlying vitreous and its surrounding ciliary pigment epithelium remain unchanged. Occasionally, highly myopic patients demonstrate a marked degree of cyst formation along the entire pars plana.

Ora Serrata Pearls

Still another change that may be noted in the fundus periphery is the ora serrata pearl. This glistening opacity ( Fig. 134-5 ), which usually forms over an oral tooth, varies from pinpoint to pinhead in size.[11] It appears in all age groups but increases significantly in incidence with advancing age.[12] Pearls are not related to other fundus pathology and are probably of developmental origin. They occur throughout the ora serrata region and

are drusen-like structures that, on pathological examination, show the staining qualities of an acid carbohydrate.

Degenerative Adult Retinoschisis

Degenerative retinoschisis, in most cases, is asymptomatic and has little clinical significance. However, in rare instances it can progress to retinal detachment. Types of retinoschisis that occur include:

• Degenerative (or adult acquired)

• X-linked

• Reticular

• Secondary

Several ocular diseases may show degrees of secondary retinoschisis; of these, diabetes, retinopathy of prematurity, and familial exudative vitreoretinopathy are three of the most important.[13]

Degenerative retinoschisis usually is bilateral, often symmetrical, and commonly bullous. It frequently first appears in the inferotemporal quadrant and may be slowly progressive.

Bullous types of retinoschisis appear clinically as thin, elevated layers of tissue, best observed in the inferotemporal periphery. The retinal vessels often are sheathed terminally, and fine white spots may occur on the inner surface. These represent the Müller fibers that traverse the schisis cavity.

Larger outer layer holes may develop over time, often with a rolled edge ( Fig. 134-6 ). A small rim of fluid, located between the outer layer and the retinal pigment epithelium, occasionally may be present. Pigmented demarcation lines are not a clinical feature of bullous retinoschisis—if present, they usually indicate longstanding nonprogressive retinal detachment.

The major complication of retinoschisis is retinal detachment. In 987 patients with retinal detachment followed up by Pecold et al.,[14] retinoschisis was present in 25, an incidence of about 2.5%.

Retinal detachment occasionally may occur when holes exist in the outer layer of the schisis. In many cases inner layer holes also occur, but these need not be present for retinal detachment to develop. The detachment begins around the outer layer holes and may progress gradually to extend beyond the area of the retinoschisis, itself. In an advanced stage it may closely resemble a typical rhegmatogenous detachment secondary to vitreous traction.[15] When progression of the schisis toward the posterior pole extends posterior to the equator, perimetry reveals an absolute

field defect, whereas the defect associated with retinal detachment is relative.

Optical coherence tomography can be helpful, as well, in differentiating retinoschisis from retinal detachment.[16] Optical coherence tomography images of retinal detachment show separation of full-thickness neurosensory retina from the retinal pigment epithelium, while retinoschisis shows the splitting within the neurosensory retina ( Fig. 134-7 ).

Byer[17] conducted a long-term natural history study of 123 consecutive, unselected patients (218 eyes) who had suffered acquired retinoschisis for from 1 to 21 years (average, 9.1 years), to ascertain the natural behavior and prognosis of this disease and formulate reasonable recommendations for its management. The quadrant of maximal involvement was the inferior temporal, and 74% of the lesions had postequatorial posterior borders. Most importantly, degenerative retinoschisis was found to be primarily asymptomatic and nonprogressive. No case of symptomatic progressive retinal detachment occurred, but 14 cases of localized, nonprogressive, and asymptomatic schisis–detachment were noted.

Byer[17] concludes that the only indication for treatment of a schisis is the symptomatic or progressive schisis–retinal detachment which threatens the macula. Laser demarcation of a schisis or treatment of the borders of outer layer retinal breaks should be avoided.[17] [18]

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Paving Stone Degeneration

Paving stone degeneration is a chronic, slowly progressive disorder which usually does not produce any symptoms or complications. Its clinical significance lies in the need to differentiate it from other peripheral disorders of greater clinical importance. Paving stone degeneration is seen more commonly in older patients and is bilateral in one third of the cases.[19]

Paving stone degeneration is characterized by well-delineated, flat yellow foci in the size range of 0.5–2.0 disc diameters ( Figs. 134-2 and 134-8 ). Irregular black pigmentation frequently is present on the margins of the lesions and red lines, which correspond to choroidal blood vessels, may traverse them. With time, the individual lesions may become confluent and form a continuous band of irregular pigment clumping. Although paving stone degeneration may be located in any quadrant, it is most common inferiorly between the equator and the ora serrata but may extend into the pars plana.

Several fundus conditions may resemble paving stone degeneration. The most important of these are inactive toxoplasmic retinochoroiditis, lattice degeneration, retinal holes, and benign hypertrophy of the retinal pigment epithelium. Toxoplasmosis is more likely to show lesions of variable size and shape, with posterior pole involvement and overlying vitreous changes.

Lattice degeneration (see below) also occurs in the peripheral retina. In contrast to paving stone degeneration, it is more common superiorly and is more likely to be equatorial, rather than adjacent to the ora serrata.

Round retinal holes may resemble focal areas of paving stone degeneration. The yellow appearance of the latter condition, with its traversing blood vessels and absence of subretinal fluid, differentiate it from a retinal hole.

Benign hypertrophy of the retinal pigment epithelium usually is located more posteriorly in the fundus and typically is pigmented more diffusely and darkly. Lacunae may be present, but only in longstanding cases in which the pigment has disappeared would it resemble paving stone degeneration.

Paving stone degeneration does not increase the risk of retinal detachment and does not require prophylactic therapy.

Cystic retinal tufts are small, pyramid-like projections of whitish retinal tissue into the vitreous cavity. They almost always occur in the vitreous base area and are believed to be congenital in origin. Cystic retinal degeneration occurs at the base of tufts. Severe vitreous traction may avulse a cystic retinal tuft; this leads to a full-thickness retinal break.

Noncystic retinal tufts are smaller, acquired, and much more common. Up to three fourths of adults manifest one or more. These tufts look like small, pointed retinal bumps within the vitreous base, most commonly in the nasal quadrants. They do not increase the risk of retinal detachment.

Traction retinal tufts project more anteriorly into the vitreous cavity because of their creation by zonular traction. These also are believed to be congenital and occur more commonly nasally, but usually develop close to the ora serrata. Small retinal breaks can occur at their base, even in the absence of a posterior vitreous separation.

Lattice Degeneration

In contrast to the degenerations previously described, lattice degeneration has greater clinical significance.[20] It is especially important because of its relationship to rhegmatogenous retinal detachment.

Ophthalmoscopically, lattice degeneration appears as one or more linear bands of retinal thinning located in the equatorial region ( Fig. 134-9 ). Fine white lines, which account for the term lattice degeneration, are present in only about 9% of lesions.[21] Pigmentary disturbances within the band of retinal thinning, however, are present in most cases. Lattice degeneration is more common superiorly and occurs less frequently near the inferior equator. It is considerably less common in the horizontal meridians. In most cases, the lesions of lattice degeneration are arranged parallel to the ora serrata.

More rarely, the lesions are orientated obliquely or even radially along retinal vessels, as in Stickler’s syndrome ( Fig. 134-10 ).

Lattice in myopic eyes may be influenced by axial elongation. Using “A” scan axial length measurement, the prevalence of lattice was greater in eyes without staphyloma in which the whole eye was elongated, versus eyes with staphyloma in which only the posterior pole was elongated.[21]

Biomicroscopy of the vitreous adjacent to lattice degeneration may reveal rather typical changes. The vitreous gel is attached

firmly to the margin of the lesion. Usually a clear pocket of liquid vitreous exists over the central thin portion of each lesion.

Retinal holes often can be observed in lattice degeneration. Two types of breaks have been recognized. Round or atrophic holes usually are found centrally within the thin portion of the lesion and usually are not associated with vitreous traction. These may lead to retinal detachment in young myopes. Horseshoe-shaped breaks occur most commonly on the posterior edge of the lesion and are associated with severe vitreous traction ( Fig. 134-11 ). In many cases, multiple breaks of both types are present. Horseshoe breaks often lead to retinal detachment.[22]

Lattice degeneration of the retina is present in about 7–8% of adult eyes. [23] [24] [25] Burton[22] has shown that patients with lattice degeneration, between 40 and 60 years of age, and with low to moderate degrees of myopia tend to develop detachments caused by premature posterior vitreous separation and traction tears. However, he points out that prophylaxis for this group is not warranted, because only 5–10% will experience detachments

Figure 134-11 Horseshoe tear on the posterior and inferior edge of lattice degeneration.

during their lives. On the other hand, this study verified the previous suspicions that those with myopia exceeding -5.0D and lattice degeneration have an increased risk of detachment during their lives. Detachments in this group tend to cluster in the second, third, and fourth decades, typically are caused by atrophic holes, are slowly progressive, and often are simultaneously bilateral. Enhanced vigilance is certainly appropriate during this time, but prophylactic treatment would be no small task because, as Burton points out, within a population of 1 million persons there are about 1150 aged 10–39 years with myopia exceeding -5.0D and lattice degeneration. Only 4 detachments annually and 40 detachments in 10 years would be expected in this highest risk group.

In an evidence-based analysis of prophylactic treatment of asymptomatic retinal breaks and lattice degeneration, a panel of vitreoretinal experts reviewed the literature published in English.[26] They concluded that there was insufficient information to strongly support prophylactic treatment of lesions other than symptomatic flap tears.